Gene expression is regulated by transcription factors, chromatin structure and higher order organization. The positioning of genes within the nucleus and with respect to each other often correlates with their expression. However, the molecular mechanisms that control gene positioning within the nucleus, and the functional significance of gene positioning, are unclear. As a model to understand gene positioning, we have focused on the molecular mechanisms by which genes move from the nucleoplasm to the nuclear periphery upon activation in Saccharomyces cerevisiae. Targeting to the nuclear periphery involves a physical interaction with the nuclear pore complex (NPC) and is mediated by cis-acting Gene Recruitment Sequences (GRSs). GRSs function as DNA zip codes: they are necessary and sufficient to induce interaction with the NPC and localization at the nuclear periphery. Furthermore, zip codes confer interchromosomal clustering of genes at the nuclear periphery. This suggests that the yeast genome encodes its spatial organization and that cis-acting DNA sequences control interchromosomal clustering of genes through interaction with the NPC. We have identified several DNA zip codes and a protein that recognizes the GRS I zip code to mediate targeting to the nuclear periphery and interchromosomal clustering. The proposed studies will 1) determine the molecular mechanism by which the GRS I DNA zip code mediates targeting to the nuclear periphery and promotes transcription, 2) determine the genome-wide scope of GRS I zip code-mediated targeting and 3) test the hypothesis that DNA zip codes impact the global organization of the yeast genome.